Chemical lasers have been made to lase at a particular wavelength. For example, a deuterium flouride laser will lase at 3.8 microns if the energy level of the deuterium fluoride is sufficiently high. This result is obtained by reacting deuterium with atomic fluorine. The atomic fluorine is produced by introducing fluorine, or a fluorine containing compound such as nitrogen trifluoride, into a first chamber containing a small quantity of a fuel such as acetylene. The fuel is rapidly oxidized to produce hydrogen fluoride plus atomic fluorine. These materials then pass through a supersonic nozzle, where an energy inversion takes place, and into a second chamber where they are mixed with deuterium and helium. The atomic flourine reacts with the deuterium to produce deuterium fluoride which lases at 3.8 microns.
One large problem in the operation of deuterium fluoride lasers is the difficulty in handling fluorine or fluorine containing compounds. Since fluorine will oxidize virtually anything, the problems of handling it can be appreciated. One workable system is made entirely of nickel. This system is first prepared for handling fluorine by the introduction into the system of a small quantity of fluorine at low pressure. The fluorine combines with the nickel to produce a thin coating of nickel fluoride on all the interior surfaces of the system. This coating is tough and is resistant to further oxidation by the fluorine as long as the system remains uncontaminated by any materials which can serve as a fuel for the fluorine. Should any contaminant be present in the system, the oxidation of the contaminant by the fluorine in the system will produce sufficient heat to burn away the nickel fluorine coating and enable the fluorine to begin burning through the nickel wall. If such an accident occurs, the burn through must be rapidly detected in order that safety measures may be taken.
One standard technique for oxidizer burn through detection has been the use of "fleak" wires. With the "fleak" wire technique, insulated wires are permanently wrapped around the oxidizer system piping. Continuity of the wires is interrupted when a burn through occurs because first the insulation and then the wires burn. The interruption in continuity is used to dump oxidizer, activate alarms, close valves, or activate damage control systems. There are various problems associated with the use of the "fleak" wire technique. For example, maintenance of the oxidizer piping system is complicated due to the presence of the "fleak" wires and the possibility exists of false alarms if the wires are broken during system maintenance. Also, nonburning oxidizer leak, e.g., a leak through a joint in the piping system, could cause the "fleak" wire insulation to ignite and this heat source could then cause the oxidizer system materials to ignite resulting in escalation of a minor burn into a major fire. Additionally, "fleak" wires cannot detect burn propagating up valve stems because "fleak" wires cannot be wrapped on moving parts. Further, joints in the piping system are also difficult to wrap to obtain 100% coverage.